Steam generator buckstay leveler systems

ABSTRACT

Apparatus is disclosed for maintaining the buckstays of a steam generator level. Upper and lower buckstays are mounted in a cantilever fashion from vertically expanding steam generator furnace walls. A first rigid member extends vertically upward from the lower buckstay and a second rigid hollow member extends vertically downward from the upper buckstay and telescopically engages the first member. The bending moment of each buckstay around its support is resisted by a horizontal force acting between the two vertical members through their telescopic engagement.

United States Patent 11 1 Shank, Jr.

[451 Jan. 21, 1975 STEAM GENERATOR BUCKSTAY LEVELER SYSTEMS [75] Inventor: John Mohr Shank, Jr., East Longmeadow, Mass.

[73] Assignee: Combustion Engineering, Inc.,

Windsor, Conn.

[22] Filed: Apr. 10, 1974 [21] Appl. No.2 459,761

[52] US. Cl. 122/6 A, 122/510 [51] Int. Cl. F22b 37/24 [58] Field of Search .122/6 A, 235 A, 494, 510

[56] References Cited UNITED STATES PATENTS 3,078,830 2/1963 Evans 122/6 A 3,203,376 8/1965 Engelhardt.. 122/6 A 3,277,870 10/1966 Reale 122/6 A 3,461,847 8/1969 Jacobs et al. 122/510 Primary ExaminerKenneth W. Sprague Attorney, Agent, or FirmFrederick A. Goettel, Jr.

[5 7] ABSTRACT Apparatus is disclosed for maintaining the buckstays of a steam generator level. Upper and lower buckstays are mounted in a cantilever fashion from vertically expanding steam generator furnace walls. A first rigid member extends vertically upward from the lower buckstay and a second rigid hollow member extends vertically downward from the upper buckstay and telescopically engages the first member. The bending moment of each buckstay around its support is resisted by a horizontal force acting between the two vertical members through their telescopic engagement.

5 Claims, 5 Drawing Figures Patented Jan. 21, 1975 3,861,360

2 Sheets-Sheet 2 FIG. 5

, 1 23 3 mr22) H i .i I '/29 L: a 2 MB r ll j 5 25 5 FIG.2 FIG. 4

STEAM GENERATOR BUCKSTAY LEVELER SYSTEMS BACKGROUND OF THE INVENTION This invention relates to steam generators and in particular to an apparatus for maintaining the buckstays thereof level without excessive bending forces on the buckstay supports. Large steam generators generally have furnaces which are lined with steam generating tubes and which are supported from the top of the unit. As the unit approaches operating temperature, the furnace structure expands vertically downward as well as horizontally. Some units operate with pressure in the furnace at all times, while others operate with negative furnace pressure. In either case, provision must be made for temporary high pressure excursions within the furnace due to minor furnace explosions or pressure increases due to the lighting of an additional burner. These pressures would tend to distort the furnace structure causing high stresses at various points and breaking insulation were not some means provided to stiffen the furnace structure. Therefore, buckstays are generally used to provide the necessary additional support. These buckstays are stiff structural members located outside the furnace structure and supported from it, thus limiting furnace wall distortion. Since furnace pressure acts on all furnace walls, the buckstays on opposite walls are connected through buckstay ties so thatthe reactions of one buckstay are resisted by the reactions of the opposing buckstay.

The vertical expansion of a large steam generator is in the order of 12 inches throughout its height. I-Iorizontal expansion of the furnace walls also occurs. The buckstays, being positioned outside the furnace, are at lower temperatures and do not expand to the same extent as the furnace walls. Therefore it has become accepted practice to support these buckstays from the furnace wall tubes at various elevations so that each buckstay moves vertically with the furnace wall tubes an amount depending on the vertical expansion of the steam generator at the particular buckstay elevation. Horizontally, the buckstay is fixed to the furnace wall at one location and permitted to slide with respect to the furnace wall at other supports. The tie between opposing buckstays is arranged in close proximity with the furnace so that the tie rod structure approaches the furnace wall temperature. As a result horizontal movement of opposing buckstays approximates the furnace expansion.

These large buckstays are supported from the furnace wall in a cantilever fashion with the buckstay weight causing a bending moment around the support. Additional forces may be imposed on the buckstays, as for example where they are used for supporting pipes or other members. Resisting the bending moment at the support would lead to high forces on the support members. Such forces in the support members would interfere with the sliding action which is required due to the relative expansion between the furnace wall structure and the buckstay, and would also produce a very high localized bending moment, and therefore high stresses in the furnace wall tubes.

It has therefore been conventional to supply other means to resist this bending moment. Generally, a vertical member extends downwardly from the upper buckstay to a lower buckstay leaving a few inches clearance from the lower buckstay. A clip on the lower buckstay interacts with the vertical member from above so as to resist the bending moment of the upper buckstay and resolve it into a force normal to the furnace wall. This is repeated throughout the height of the unit with three of four vertical members being positioned between each pair of buckstays. The lowest buckstay has vertical members extending upwardly as well as downwardly from the buckstay above. In this fashion, the bending moment of the lower buckstay is resolved into a normal force at the buckstay elevation above and vice versa.

With such an arrangement, vertical buckstay levelers must pass through the entire height of the unit in segments, therefore producing a general clutter and limited access throughout the entire height of the unit. Considerable material is also required since these vertical members must pass through the entire height of the unit. Another arrangement for resistingthe bending moment due to buckstay weight is disclosed in US. Pat. No. 3,461,847. In this patent, bending moments of an upper and lower buckstay are used to counteract one another through vertically extending rigid members. A first member extends downward from an upper buckstay and a second member extends upward from an un derlying buckstay. The two members overlap and en gage one another in a manner whereby horizontal forces may be transmitted between the members at a location where the bending moment for each buckstay supplies the proper resisting force for the other buckstay. This arrangement is repeated throughout the elevation of the steam generator with the buckstays operating in pairs, thereby limiting the number of vertical members needed to one-half of those required in the other described arrangements.

With such an arrangement, the means for transmitting the horizontal forces between the overlapping vertically extending members have included mating flat surfaces, and a bolted connection between the two vertically extending members. While ideally an arrangement employing abutting flat surfaces between the two beams would result in a sliding surface contact between the two, in reality a horizontal line contact most probably exists in either the upper end of the lower beam or the lower end of the upper beam. Such a condition, taken with the fact that the two buckstays involved may be moving at different rates or at different magnitudes due to thermal expansion differentials, results in a rather precarious contact between the two beams. As a result, a very real possibility exists that the beams could slip out of engagement with one another and become ineffective. The possibility of two beams slipping out of engagement would seem to be eliminated with the use of several bolted connections between the beams. This arrangement, however, introduces several other problems the most prominent of which is the problem of properly aligning the holes in the beams for fabrication. Another drawback of such an arrangement is the large bending load to which the bolts are subjected. If overstressed the bolts would be the first element to fail, resulting in an abutting arrangement as described above with its inherent drawbacks.

SUMMARY OF THE INVENTION The present invention overcomes the disadvantages of the prior means for transmitting the horizontal forces in a buckstay leveler system of the type wherein bending moments of an upper and lower buckstay are used to counteract one another through vertically extending rigid members. The upper and lower vertically extending rigid members are constructed and arranged to engage one another in a telescoping fashion. Such an arrangement results in a stable, simple engagement between the opposing members which has none of the disadvantages of the prior art arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view through a steam generator furnace showing the general arrangement of buckstays and buckstay levelers.

FIG. 2 is a side elevation of a buckstay leveler according to the present invention.

FIG. 3 is a sectional view taken along the Line 33 of FIG. 2.

FIG. 4 is a side elevation of a second embodiment of a buckstay leveler according to the present invention.

FIG. 5 is a sectional view taken along the Line 5-5 of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBOBIMENTS FIG. 1 being a sectional plan view of a steam generator shows furnace 2 which has its walls lined by a plurality of vertical steam generating tubes 3. These tubes extend throughout the height of the steam generator and expand longitudinally as the unit comes up to operating temperature. Since the parallel furnace wall tubes are interconnected laterally by welding adjacent tubes together, the furnace will also expand horizontally. To retain the square furnace shape under internal furnace pressure, opposing buckstays 4 and 5 are positioned on opposing walls while opposing buckstays 6 and 7 are positioned on the adjacent pair of opposing walls. These buckstays are supplied at a number of elevations and are supported in a manner illustrated in FIGS. 2 and 4. An increased furnace pressure tends to force the tubes outwardly against buckstay 4, and this buckstay remaining rigid prevents the tubes from moving outward. Buckstay 5 performs the same function on the opposing wall. Buckstay ties 8 are connected to each end of each buckstay so that the force tending to move buckstay 5 to the left is opposed by the force tending to move buckstay 4 to the right. These buckstay ties 8 are formed in several parts with one part 9 maintained in close relationship with the furnace wall so that it approaches the furnace tube temperature through their co-extensive portion, and the buckstay tie portion 9'expands to the same extent that the furnace expands horizontally. This permits the buckstays to move outwardly from each other as the furnace expands whereby the buckstays maintain the same spaced relationship with their adjacent furnace wall tubes.

Referring to FIG. 2, lower buckstay 4 is supported from the furnace wall tubes 3 by stirrup l7 and bolt 18. A fixed connection is provided between the stirrups and buckstays, near the'centerline of the furnace while at other locations a slotted hole is provided so that furnace may expand horizontally with relation to the buckstay. The weight of the buckstay. 4 produces a clockwise bending moment around the supporting bolt.

18. If not counteracted, this bending moment would subject the tubes 3 to high bending stresses; and since these tubes contain high pressure water and steam and are exposed to furnace radiation, such high-stresses are intolerable.

Referring still to FIG. 2, an upper buckstay 22 is similarly supported from furnace tubes 3 through a second stirrup 23 and bolt 24. This buckstay 22 similarly has a clockwise bending moment around its support caused by its own weight. A rigid circular pipe section 25 is welded to the lower buckstay 4 and extends vertically upward therefrom. A second rigid circular pipe section 27 is welded to the upper buckstay 22. This second pipe 27 has a larger inner diameter than the outer diameter of pipe 25 and extends vertically downward and telescopically receives the upper end of the pipe 25.

The clockwise bending moment of the buckstay 4 accordingly causes the vertically extending member 25 to tend to rotate in a clockwise direction, that is to the right-hand side. Similarly, the clockwise bending moment of the buckstay 22 causes the vertically extending member 27 to tend to rotate in a clockwise direction. In this case to the left-hand side. As a result of the tendency of the beams 25, 27 to move in opposite directions they are caused to contact one another in the region of telescopic engagement and the oppositely directed horizontal forces of the two beams will tend to cancel one another, thus resisting the bending moments caused by the weight of the two buckstay members 22, 4.

Because the two vertically extending pipe members 25 and 27 remain at ambient temperature while the furnace wall tubes 3 are heated to some 700F, it is possible that the two buckstay members 22, 4 may be expanding vertically at a differential rate, this differential rate of movement is accommodated by the sliding engagement of the telescopically engaged upper and lower vertically extending pipe members25, 27. In theory, the point of contact between the two members, as indicated at elevation 28, is selected so that the horizontal forces imposed are sufficient to counteract the bending moments of each buckstay. Where the buckstays are of equal weight and have equal moments, the distance between the center of the web portion of the upper buckstay 22 and the intermediate elevation 28 designated by L1 is equal to the vertical distance between the intermediate elevation 28 and the center of the web portion of the lower buckstay 4 as designated by L2. Where different bending moments exist in the two buckstays, the vertical distances L1 and L2 will be inverse proportion to the bending moment of each buckstay around its respective support. If additional loads are imposed on the buckstays, such as piping support, these loads will be considered in determining L1 and L2 so as to arrive at the proper intermediate elevation 28, so that the horizontal forces may be reacted against one another in order to oppose the bending moments of each of the buckstays.

In a similar fashion buckstays 5, 6 and 7 are coupled with corresponding buckstays at an upper elevation and use a construction similar to that illustrated in FIGS. 2 and 3. The remaining buckstays on the steam generator at various elevations are treated in pairs in the same manner as buckstays 4 and 22. The horizontal force to the left imposed on vertically extending pipe 25 results in a force towards the furnace wall on the lower buckstay 4. The same force acting in the other direction from vertically extending pipe 27 imposes a force away from the furnace wall on the upper buckstay 22. In order to avoid any necessity of the furnace wall structure taking these horizontal loads, the identical arrangement, as shown in FIG. 2, is used on the opposite side of the unit with buckstay 5 being directly opposite of buckstay 4, and with another buckstay being directly opposite buckstay 22. The horizontal force imposed on the upper and lower buckstays is thus transmitted through tie rods 8, 9, precluding any need for the introduction of these horizontal forces into the furnace wall tubes 3.

FIGS. 4 and 5 illustrate an alternate arrangement wherein all of the structural features of the buckstay leveler system are the same as those described in FIGS. 2 and 3, with the exception that the vertically extending pipe 29 extending downwardly from the upper buckstay 22 is fabricated from a square channel. This square channel 29 similarly, telescopically and slidably engages the pipe 25 extending upwardly from the lower buckstay 4. The relationship between the moments and corresponding forces are the same as in the first embodiment.

While we have illustrated and described preferred embodiments of our invention it is to be understood that such is merely illustrative and not restrictive, and that variations and modifications may be made therein without departing from the spirit and scope of the invention. We, therefore, do not wish to be limited to the precise details set forth, but desire to avail ourselves of such changes as fall within the purview of our invention.

What is claimed is:

1. Apparatus for maintaining level the buckstays of a steam generator having a vertically'expanding furnace structure, said steam generator having a first buckstay at a lower elevation, a first support supporting said first buckstay from the furnace structure in a cantilever fashion; said steam generator also having a second buckstay at an upper elevation, and a second support supporting said second buckstay from the furnace structure in a cantilever fashion comprising: a first member rigidly fastened to said first buckstay and extending upwardly; an a second member rigidly fastened to said buckstay and extending downwardly and slidably and telescopingly engaging said first member, said telescopic engagement of said first and second members permitting transmission of horizontal force said first and second members at an intermediate elevation between said first and second buckstay elevation; said intermediate elevation being a vertical distance from said first and second supports in inverse proportion to the bending moment of said first and second buckstays around their respective supports.

2. Apparatus as in claim 1 wherein said first member comprises a first pipe of circular cross section welded to said first buckstay and extending vertically upward and said second member comprises a second circular pipe having an inner diameter greater than the outer diameter of said first pipe and extending vertically downward in telescopic relation with said first pipe.

3. Apparatus as in claim 1 wherein said first member comprises a pipe of circular cross section welded to said first buckstay and extending vertically upward and said second member comprises a square tube having an inner flat-to-fiat dimension greater than the outer diameter of said pipe and extending vertically downward in telescopic relation to said pipe.

4. Apparatus as in claim 1 wherein the bending moment of each buckstay around its respective support is equal and the horizontal force is transmitted at an elevation equi-distant from said first and second buckstay elevations.

5. Apparatus as in claim 1 wherein said first and second buckstays, said first and second supports, and said first and second members comprise a buckstay structure; having also an identical buckstay structure on the opposite side of the furnace structure; buckstay ties connecting each end of the upper buckstay on one side of the furnace to the corresponding end of the upper buckstay on the other side of the furnace; and buckstay ties connecting each end of the lower buckstay on one side of the furnace to the corresponding ends of the buckstay on the opposite of the furnace.

UNITED STATES PATENT OFFICE CERTIFICATE @F CORRECTIQN Q PATENT NO. 3,861,360

DATED 1 January 21, 1975 INVENTOR(S) 1 J hn M h shank, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent 3 are hereby corrected as shown below:

Column 1, line %6 following "furnace" insert -wall.

Column r, line 38 following second occurrence of "equal" insert -bending- I! H I Column l, line +5 following be insert --1n.

Column 5, line &0 following "said" insert -second-.

0i Column 6, line 3 following "force" insert -between--.

srgncd and gated this twentieth a O [SEAL] D y f Apr1lI1976 0t Arrest.

RUTH c. MfiSON c. MARSHALL DANN Altesmrg ()jjrcer (mnmissivm'r Hf Parents and Trademarks I 

1. Apparatus for maintaining level the buckstays of a steam generator having a vertically expanding furnace structure, said steam generator having a first buckstay at a lower elevation, a first support supporting said first buckstay from the furnace structure in a cantilever fashion; said steam generator also having a second buckstay at an upper elevation, and a second support supporting said second buckstay from the furnace structure in a cantilever fashion comprising: a first member rigidly fastened to said first buckstay and extending upwardly; an a second member rigidly fastened to said buckstay and extending downwardly and slidably and telescopingly engaging said first member, said telescopic engagement of said first and second members permitting transmission of horizontal force said first and second members at an intermediate elevation between said first and second buckstay elevation; said intermediate elevation being a vertical distance from said first and second supports in inverse proportion to the bending moment of said first and second buckstays around their respective supports.
 2. Apparatus as in claim 1 wherein said first member comprises a first pipe of circular cross section welded to said first buckstay and extending vertically upward and said second member comprises a second circular pipe having an inner diameter greater than the outer diameter of said first pipe and extending vertically downward in telescopic relation with said first pipe.
 3. Apparatus as in claim 1 wherein said first member comprises a pipe of circular cross section welded to said first buckstay and extending vertically upward and said second member comprises a square tube having an inner flat-to-flat dimension greater than the outer diameter of said pipe and extending vertically downward in telescopic relation to said pipe.
 4. Apparatus as in claim 1 wherein the bending moment of each buckstay around its respective support is equal and the horizontal force is transmitted at an elevation equi-distant from said first and second buckstay elevations.
 5. Apparatus as in claim 1 wherein said first and second buckstays, said first and second supports, and said first and second members comprise a buckstay structure; having also an identical buckstay structure on the opposite side of the furnace structure; buckstay ties connecting each end of the upper buckstay on one side of the furnace to the corresponding end of the upper buckstay on the other side of the furnace; and buckstay ties connecting each end of the lower buckstay on one side of the furnace to the corresponding ends of the buckstay on the opposite of the furnace. 